Abstract
The Cyclone Global Navigation Satellite System (CYGNSS) is a
multi-satellite constellation that utilizes Global Positioning System
(GPS) reflectometry to retrieve near-surface wind speeds over the ocean.
While CYGNSS is primarily aimed at measuring wind speeds in tropical
cyclones, our research has established that the mission may also provide
valuable insight into the relationships between wind-driven surface
fluxes and general tropical oceanic convection. Currently, we are
examining organized tropical convection using a mixture of CYGNSS level
1 through level 3 data, IMERG (Integrated Multi-satellite Retrievals for
Global Precipitation Measurement), and other ancillary datasets
(including buoys, GPM level 1 and 2 data, as well as ground-based
radar). In addition, observing system experiments (OSEs) are being
performed using hybrid three-dimensional variational assimilation to
ingest CYGNSS observations into a limited-domain, convection-resolving
model. Our focus for now is on case studies of convective evolution, but
we will also report on progress toward statistical analysis of
convection sampled by CYGNSS. Our working hypothesis is that the typical
mature phase of organized tropical convection is marked by the
development of a sharp gust-front boundary from an originally spatially
broader but weaker wind speed change associated with precipitation. This
increase in the wind gradient, which we demonstrate is observable by
CYGNSS, likely helps to focus enhanced turbulent fluxes of
convection-sustaining heat and moisture near the leading edge of the
convective system where they are more easily ingested by the updraft.
Progress on the testing and refinement of this hypothesis, using a
mixture of observations and modeling, will be reported.